The identification of human tumor suppressor genes has led to new insights into the mechanisms of human cancer development. Most of the known tumor suppressor genes were isolated by determining their chromosomal location using molecular markers or cytogenetics. We have taken the opposite approach by using a biological assay, tumor suppression, to map the locations of functional tumor suppressor genes via monochromosome transfer. In this manner, we have mapped a tumor suppressor gene for a Wilms' tumor cell line to a region of chromosome 11p15.5 flanked by two anonymous markers. Our preliminary physical map of this area suggests that this region contains less than 1000 kilobases (kb). Based on similarities between our functional studies and those concerning the RB and p53 genes, we propose that this gene represents another cell cycle control gene. To test this hypothesis, we will use positional cloning techniques to identify candidates for the functional tumor suppressor gene. We have gathered both cosmids and yeast artificial chromosomes (YACs) from this area for probing a fetal kidney cDNA library. To sort through this group, we will look for genes with abnormalities in the Wilms' tumor cell line. Alternatively, we will chose genes which show increased expression in the microcell hybrids relative to the parental cell line. The ultimate identification of this tumor suppressor gene will depend on its ability to suppress tumorigenicity in the Wilms' tumor cell line. Once we have isolated the tumor suppressor gene, we will search for sequence homologies with other known genes to further delineate its functions. After developing immunological reagents for the gene product, we will characterize expression of the gene in Wilms' tumor cell lines, normal cells and non-tumorigenic microcell hybrids. We will also determine its patterns of expression in developing human fetal material and in different types of normal human tissues. Finally, we will search for abnormalities in this gene in tumor samples from Wilms' tumor patients as well as patients with other malignant and/or genetic diseases which map to this same region of chromosome 11. The isolation of this tumor suppressor gene will represent the first such gene identified by a functional assay. The availability of another cell cycle control gene would broaden our understanding of tumor suppressor gene functions and may provide important clues about the process of normal mammalian tissue development.